This invention related to a circuit, especially related to a circuit for safely turning off an electronic switch when fault happens.
A converter is widely used in a power converting circuit for converting electrical power from the power source to the electrical power to the load. For example, an inverter can convert a DC power to an AC power for providing to an AC load. A rectifier can convert an AC power to a DC power for providing to a DC load. A DC/DC converter can convert a DC power to another DC power. Generally, the converters include multiple switching modules. Power converting process can be achieved by turning on and off the switching modules by a suitable control system. For some power converting system with a request of high voltage such as high voltage pump, high voltage compressor, etc., a current with a high voltage will flow through each switching branch. Typically, the switching modules in each switching branch include thyristors such as Insulated Gate Bipolar Transistor (IGBT). Under some circumstances, if only a switch is used in each switching branch, the IGBT is not able to bear the high voltage. In order to avoid the damage to the switch, at least two IGBTs are coupled in series in the switching branch to share the high voltage and a synchronous control is implemented. When fault (e.g., a short circuit fault) occurs, the IGBT(s) is needed to be turned off and an over voltage caused by a quick change of the current may damage the IGBT(s). After the occurrence of the short circuit fault, a serious problem of voltage imbalance will exist when turning off the at least two IGBTs and even damage at least one of the IGBTs which bears a higher turn-off voltage. Considering the characteristics of IGBT and the accuracy of the control system, conventional short circuit protection method usually cost a lot of money or using a corresponding complex circuit.
Therefore, a new low-cost and simple circuit is needed to solve the above problems.